As an alternative or add-on to satellite-based positioning systems, positioning systems in which a present position of a terminal is estimated based on an identification of coverage areas that can currently be detected by the terminal have gained recent interest. For instance, a terminal may identify all currently detectable coverage areas, which are provided by Coverage-Providing Entities (CPEs) (such as for instance base stations of a cellular Communication System (CS), or Wireless Local Area Network (WLAN) Access Points (APs)), and consult a local or remote database that provides Coverage Area Representations (CARs, e.g. models for the coverage areas) for the identified coverage areas.
In a simple case, such a CAR may at least comprise the position of the CPE (e.g. a WLAN access point) that provides the coverage area detected by the terminal. In more elaborate cases, a CAR may for instance describe the position, dimensions and orientation of an elliptical model of the coverage area provided by the CPE (e.g. a base station of a cellular mobile communication system).
For instance, given that (only) the positions of the CPEs of the detected coverage areas are known at the terminal, and distances from the terminal to the heard CPEs can be estimated, the terminal's position can be estimated through triangulation. The distance between a terminal and the heard CPEs can for instance be estimated based on the path loss using a channel model (i.e. how much the signal attenuates between the terminal and the CPE) or based on timing (or round-trip timing) measurements (i.e. information expressing how long signals propagate between terminal and CPE).
Alternatively, if more elaborate CARs are available are known, a terminal may pick the CARs for the detected coverage areas and find the intersection of these CARs. The terminal can then be assigned a position that is, for instance, the center-of-mass of the intersection area. Similarly, an error estimate for the position estimate can be given, for example, based on the size of the intersection.
The CARs can for instance be generated based on a plurality of detections performed by terminals that are able to determine their current position (e.g. by means of satellite-based positioning) and to identify the coverage areas that they can currently detect. Such information can then be assembled and sent (as a so-called fingerprint) to a server that selectively analyzes the fingerprints received with respect to each coverage area. For instance, from all fingerprints received, the server may extract all positions at which terminals were able to detect a specific coverage area. A representation of the boundary and/or shape of this plurality of positions, e.g. an ellipse fitted to this boundary and/or the mean value plus covariance of the samples, then already can serve as a CAR for this specific coverage area. Similarly, respective CARs for further coverage areas can be extracted.